1. Field of the Invention
The present invention relates to a unit control oriented communication device for exchanging information between a group of units scattered inside and outside of a system and a main control section for controlling the group of units, and more particularly, to an optical radio communication device which utilizes light (hereinafter referred to as a wireless optical communication device).
2. Description of the Related Art
Conventionally, a copier, a FAX, or a laser beam printer (hereinafter referred to as an LBP) is composed of a main control portion for controlling the entire system and a group of units scattered inside and outside of the system. The group of units are each composed of an output control section comprising a motor, a fan or an actuator, such as a solenoid, and an input control section comprising switches and sensors. In that case, the input/output control sections are respectively controlled mainly through an I/O port of a CPU. Since these input/output control subjects are scattered within the system, they are connected with each other through a wire harness. These input/output control subjects are connected to the main control portion independently from each other (hereinafter referred to as parallel connection). Alternatively, the main control portion serially transfers data to each unit utilizing serial communication. Each unit conducts "serial-parallel conversion", by which the control subjects are connected to the main control portion independently.
An example of the aforementioned parallel connection will be described. In the case of a system shown in FIGS. 31 and 32 which consists of units 406 and 407, the unit 406 serves as a control unit, and the unit 407 serves as a controlled unit (on which a mechanism part, such as a solenoid, is mounted). In this case, a CPU 301 is connected through signal lines directly to respective mechanism portions 401, 402, 403 and 404 in the controlled unit (FIG. 31) to control them. Although an amplification means or the like, such as a transistor, is disposed between the control unit 406 and the controlled unit in an actual circuit configuration, it is omitted in FIGS. 31 and 32 in order to explain the flow of signals.
In another case, the subjects to be controlled are controlled by the CPU 301 through an I/O expansion device 301a, as shown in FIG. 32.
In the above-described methods, the number of signal lines (signal line bundles) increases in proportion to the number of subjects to be controlled, and this makes reduction in the overall size of the system difficult.
That is, as the number of functions of the system increases, the number of input/output control subjects increases, thereby increasing the number of control lines for parallel connection. As a result, production cost increases, and assembly efficiency deteriorates. Hence, the general trend is toward an arrangement of scattered output and input signals into a plurality of physical or functional blocks and transmission of signals by the serial communication.
Serial communication commonly conducted between the main control portion and the group of units is asynchronous serial communication, called UART, or clock synchronizing type serial communication.
In the former type of serial communication, a single frame consists of twelve bits, including a starting bit (1 bit), a data bit, and a stop bit (2 bits). The transmission side outputs a signal representing one frame with a predetermined period. The reception side reads data representing one frame at the same period as the transmission side when it confirms the starting bit.
In the latter type of serial communication, a single frame consists of eight bits. The transmission side outputs a signal representing one frame with a clock signal and a data signal separately through corresponding paths. The reception side reads the status of the data signal at a timing at which a clock signal rises or falls and receives data representing one frame.
However, the above-described conventional methods have the following disadvantages.
(1) In the method of decreasing the number of control lines by conducting serial transfer from the main control portion utilizing serial communication such as UART, a malfunction may occur due to the erroneous transfer caused by noise generated in the system, or the control line may generate radiation noises in the form of an electric field as the serial transfer speed increases.
To overcome this disadvantage, radio transmission of data using light has been considered.
In the field of electric appliances, radio transmission of data using light, so-called remote control, has been conducted. However, such a system is of the unidirectional type (in which data is transmitted only from the transmission device to the reception device). Furthermore, the data transmission speed is such that it cannot catch up with the transmission speed of input/output signals in, for example, a copier, FAX or LBP. Furthermore, when optical transfer is conducted at a relatively high speed in two directions, collision of light or erroneous transmission caused by a disturbance may occur. Also, the existence or non-existence of the reception device cannot be determined at the main control portion. Furthermore, adjustment or checking conducted during the assembly is troublesome, and reduces efficiency.
(2) Although there is no problem in the case of transmission of a signal consisting of one bit, when a signal consisting of a plurality of bits is to be transmitted, all the bits do not change at one time, and transmission of an erroneous signal may thus occur unless data latching is not adjusted.
This problem will be explained in detail with reference to FIG. 33.
In the case shown in FIG. 33, communication is made between the units 406 and 407 through a communication line 405. The communication line 406 may be parallel or serial. This choice is made depending on the transfer speed or the application of the transfer. Although this communication is more advantageous when a plurality of units 407 to be controlled exist, the units 406 and 407 make one-to-one correspondence in this case for the ease of explanation.
A CPU 301 and a transmission means 409 function independently. The CPU 301 sends transmit data to a transmission register 408. The transmission means 409 transfers the content of the transmission register 408 to the unit 407 at predetermined time intervals. A reception means 302 transfers the received data to the individual mechanism sections 401, 402, 403 and 404.
In order to control the unit 407, monitoring of an external status is required. Fetching of externally monitored signals to the CPU 301 through the communication line will be described below with reference to FIG. 34.
A signal from sensors (for example, microswitches or photo-interruptors) 410, 411, 412 and 413 is transferred from a transmission means 303 to a reception means 414. A communication line 416 which connects the transmission means 303 and the reception means 414 may be of the parallel or the serial type. The reception means 414 writes receive data in a reception register 415. The reception register 415 is connected to the CPU 301, and the CPU 301 can read the content thereof at a desired time. That is, new data (which represents the state of the mechanism sections 410, 411, 412 and 413, in this case) is kept stored in the reception register 415.
The transmission register 408 and the reception register 415 will be described in more detail.
FIG. 35 explains the operation of the transmission register 408. The transmission register 408 is required for the CPU 301 and the transmission means 409 being operated independently. The number of bits for the register 408 must be made to coincide with the total number of bits in the destination unit.
In order to conduct mapping between the transmission register 408 and the CPU 301 and thereby assign a certain address of the CPU 301 to the register 408, a write signal 438 is created by decoding an address signal on an address bus 434 by means of a decoder 435 and then by performing an AND operation on the decoded address signal and a write signal 433. The transmit data is transferred to the transmission register 408 synchronously with the write signal 438.
The transmission means 409 latches the content of the transmission register 408 synchronously with a latch signal 439 from a control circuit 437. That is, the transmission means 409 takes in data from the transmission register 408 to its latches corresponding to the bits of the data, e.g., the data in a latch 417 is latched to a latch 425, the data in a latch 418 is latched to a latch 426, and so on. Thereafter, the transmission means 409 conducts transmission operation independently.
Next, the reception register 415 will be described in detail with reference to FIG. 36. Once the reception means 414 receives data from the transmission means 303 of the external unit 407, it outputs a write pulse 452 and latches the data in latches 440 to 447 of the reception register 415. The receive data is read by the CPU 301 from the reception register 415 by means of a signal obtained by decoding an address signal 434 output from the CPU 301 for mapping by a decoder 448 and then by performing an AND operation on the decoded signal and a read signal 449.
Unit control is thus performed through the communication lines 405 and 416.
In a case where data is transmitted from the CPU 301 to the unit 407, the timing of the write signal 438 of the CPU 301 may differ from that of the read-out signal 439 of the unit, as shown in FIG. 37. In that case, data 453 output from the CPU 301 may be latched in the transmission register 408 at a time indicated by data 454 in FIG. 37, and that data may be read in the transmission means 409 at a time indicated by data 455 in FIG. 37. Erroneous transmission of the data does not occur when the data is read in the transmission means 409 at a time other than a transition of the data 454, as in the case of the above-described case. The same thing applies to the case in which data is transmitted to the CPU 301. In the case shown in FIG. 36, data 457 from the reception means 414 is latched in the reception register 415 by the write signal 452 at a time indicated by data 456 in FIG. 38. The latched data 456 is taken in the CPU 301 by the read signal 451 at a time indicated by data 458 in FIG. 39. There is no problem in the case shown in FIG. 38 in which the data is taken in the CPU 301 at a time other than a transition of the data 456.
However, the above-described conventional technique has the following disadvantages.
In the case of the signal whose one bit has a significance, like the signals 401 and 402 shown in FIG. 33 and like the signals 410 and 411 shown in FIG. 34, there is no problem. However, in the case of a significant signal consisting of a plurality of bits, since transition does not occur on the individual bits simultaneously, erroneous transmission may occur.
That is, in a case where the transmission means 409 latches data at the transition of the data 454, as shown in FIG. 39, the transmit data subsequent to a reference number 459 is not guaranteed. Also, in a case where the CPU 301 reads in data at the transition of the data 456, as shown in FIG. 40, data subsequent to 460 is not guaranteed.
In order to avoid this disadvantage, a handshake may be conducted in terms of software or hardware between the CPU 301 and the transmission means 409 or between the CPU 301 and the reception means 414. However, this requires complicated additional circuits and hence increases the production cost of the system.
(3) Parallel connection between a communication device (hereinafter referred to as a master) of the main control portion and the communication device (hereinafter referred to as a slave) of each of the group of units is easily affected by noise or the like. In the case of a series connection, the unit to be controlled independently may affect or be affected by other units.
When the operation of a system is to be controlled utilizing the serial communication for the exchange of information between the central processing unit for executing the main control of the system and the individual units which scatter in the system, the system is conventionally structured in the manner shown in FIG. 45.
In FIG. 45, a master 550 is a main communication device in the central processing unit which controls serial communication. Slaves 551 to 554 are sub-communication devices in the individual units scattered in the system which conduct serial communication and executes information exchange.
In this serial communication, the master and slaves make 1-to-N correspondence. Therefore, exchange of serial data signal is conducted between the main communication device and the individual sub-communication devices which are parallel-connected to the main communication device independently.
Therefore, in the above-described conventional system, the communication lines for the serial data signal are extended over a long distance because of parallel connection, causing malfunction to occur due to the noise generated within the system. Furthermore, its drive ability of the master communication device must be enhanced by providing a drive means in the master communication device. This may increase the production cost.
Furthermore, in the case of a unit that can be detachably mounted by a user, the serial data signal lines may directly receive external noise from the connector of the detachably mounted unit, which leads to breakage of the main control unit. This increases maintenance cost.
Furthermore, in a case where an abnormality occurs in the system, the sub-communication device in a certain unit may be forcibly reset in order to turn off all the actuators or the like connected to that sub-communication device. In another unit, serial communication may be continued for anomaly processing. These necessitate independent parallel connection between the main communication device and the individual sub-communication devices. For example, in a laser beam printer, if paper jam occurs during the paper feeding operation, high-voltage output must be stopped instantaneously in order to protect a light-sensitive drum or the like. However, interruption of the paper feeding logic and restarting of the paper feed after jam has been removed may cause a jam again.